/*
 * Copyright (c) 2011-2020, hubin (jobob@qq.com).
 * <p>
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.baomidou.kisso.common.encrypt;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.math.BigInteger;

/**
 * A bare-minimum ASN.1 DER decoder, just having enough functions to decode
 * PKCS#1 private keys. Especially, it doesn't handle explicitly tagged types
 * with an outer tag.
 *
 * <p/>
 * This parser can only handle one layer. To parse nested constructs, get a new
 * parser for each layer using <code>Asn1Object.getParser()</code>.
 *
 * <p/>
 * There are many DER decoders in JRE but using them will tie this program to a
 * specific JCE/JVM.
 *
 * @author zhang
 */
public class DerParser {
  // Classes
  public final static int UNIVERSAL = 0x00;
  public final static int APPLICATION = 0x40;
  public final static int CONTEXT = 0x80;
  public final static int PRIVATE = 0xC0;

  // Constructed Flag
  public final static int CONSTRUCTED = 0x20;

  /**
   * Tag and data types
   */
  public final static int ANY = 0x00;
  public final static int BOOLEAN = 0x01;
  public final static int INTEGER = 0x02;
  public final static int BIT_STRING = 0x03;
  public final static int OCTET_STRING = 0x04;
  public final static int NULL = 0x05;
  public final static int OBJECT_IDENTIFIER = 0x06;
  public final static int REAL = 0x09;
  public final static int ENUMERATED = 0x0a;
  public final static int RELATIVE_OID = 0x0d;

  public final static int SEQUENCE = 0x10;
  public final static int SET = 0x11;

  public final static int NUMERIC_STRING = 0x12;
  public final static int PRINTABLE_STRING = 0x13;
  public final static int T61_STRING = 0x14;
  public final static int VIDEOTEX_STRING = 0x15;
  public final static int IA5_STRING = 0x16;
  public final static int GRAPHIC_STRING = 0x19;
  public final static int ISO646_STRING = 0x1A;
  public final static int GENERAL_STRING = 0x1B;

  public final static int UTF8_STRING = 0x0C;
  public final static int UNIVERSAL_STRING = 0x1C;
  public final static int BMP_STRING = 0x1E;

  public final static int UTC_TIME = 0x17;
  public final static int GENERALIZED_TIME = 0x18;

  protected final InputStream in;

  /**
   * Create a new DER decoder from an input stream.
   *
   * @param in
   *            The DER encoded stream
   */
  public DerParser(final InputStream in) throws IOException {
    this.in = in;
  }

  /**
   * Create a new DER decoder from a byte array.
   *
   * @param bytes the encoded bytes
   */
  public DerParser(final byte[] bytes) throws IOException {
    this(new ByteArrayInputStream(bytes));
  }

  /**
   * Read next object. If it's constructed, the value holds encoded content
   * and it should be parsed by a new parser from
   * <code>Asn1Object.getParser</code>.
   */
  public Asn1Object read() throws IOException {
    final int tag = in.read();

    if (tag == -1) {
      throw new IOException("Invalid DER: stream too short, missing tag");
    }

    final int length = getLength();

    final byte[] value = new byte[length];
    final int n = in.read(value);

    if (n < length) {
      throw new IOException("Invalid DER: stream too short, missing value");
    }
    return new Asn1Object(tag, length, value);
  }

  /**
   * Decode the length of the field. Can only support length encoding up to 4
   * octets.
   *
   * <p/>
   * In BER/DER encoding, length can be encoded in 2 forms,
   * <ul>
   * <li>Short form. One octet. Bit 8 has value "0" and bits 7-1 give the
   * length.
   * <li>Long form. Two to 127 octets (only 4 is supported here). Bit 8 of
   * first octet has value "1" and bits 7-1 give the number of additional
   * length octets. Second and following octets give the length, base 256,
   * most significant digit first.
   * </ul>
   *
   * @return The length as integer
   */
  private int getLength() throws IOException {

    final int i = in.read();

    if (i == -1) {
      throw new IOException("Invalid DER: length missing");
    }

    // A single byte short length
    if ((i & ~0x7F) == 0) {
      return i;
    }

    final int num = i & 0x7F;

    // We can't handle length longer than 4 bytes
    if (i >= 0xFF || num > 4) {
      throw new IOException("Invalid DER: length field too big (" + i + ")");
    }

    final byte[] bytes = new byte[num];
    final int n = in.read(bytes);

    if (n < num) {
      throw new IOException("Invalid DER: length too short");
    }
    return new BigInteger(1, bytes).intValue();
  }
}
